1. Field of the Invention
The present invention relates to a method for forming post bumps; and, more particularly, to a method for forming post bumps in which metal post is formed, and a solder ball is formed on the metal post.
2. Description of the Related Art
A packaging technology of integrated circuits is being continuously developed to satisfy the requirement of miniaturization and reliable mounting in semiconductor industries.
For example, the requirement of miniaturization brings out mounting development of the packaging technology in which integrated circuits are manufactured to become as small as a chip. Moreover, the requirement of reliable mounting gives much interest on a packaging technology which can improve mechanical and electrical reliability after mounting, and efficiency of mounting work.
As for a typical example of the package miniaturization, a Ball Grid Array (hereinafter, referred to as ‘BGA’) may be exemplified. The size of the entire BGA package is the same as that of a semiconductor chip, or is almost similar to that of a semiconductor chip.
In particular, a BGA uses a solder ball to mount electronic devices on a Printed Circuit Board (PCB), so it is possible to remarkably reduce mounting area.
With the recent trend toward high integration of semiconductor chips, there has been much use of Fine Pitch Ball Grid Array (FBGA) package in which fine pitches between signal/power input/output pins are made and mounting area is reduced while electrical connection to an external circuit is achievable by a solder ball.
In addition, there has been developed a post bump formation scheme for using copper electroplating instead of a solder paste or a solder ball, in order to make a bump with a finer pitch than is made by a solder bump formation scheme.
When a post bump is formed by using copper plating, it is necessary to form posts with the same height in copper electroplating. In order to form the posts with the same height, it is necessary to reduce plating variation. However, since plated-region is very small and plated-portion is concentrated on a central portion of a product, currents are concentrated in a plating process, which results in non-uniformity of post bump's height and plating variation.